prompt = "\nWhat topping would you like on your pizza?"
prompt += "\nEnter 'quit' when you are finished: "
while True:
    topping = input(prompt) # 提示用户输入一系列比萨配料
    print(f"Adding {topping}.")
    if topping == 'quit': # 如果用户输入的是'quit'，则退出循环
        break